1. Field of the Invention
The present invention relates to a printed inductance comprising a flexible insulating supporting-plate and at least one first rectangular conductive spiral supported by one of the faces of the supporting-plate.
2. Description of the Prior Art
Conventional inductances of coil type which form magnetic circuits of small thickness which can be employed in the reading heads of telecopier devices, for example, are quite often unable to be produced by means of automatic equipment because of the high ratio between the widths and the thickness of the straight sections of the coil. The minimum diameter of the winding wires which are employed in known winding machines if still much too large for producing thin magnetic circuits.
In order to correct these disadvantages spiral-formed inductances have been manufactured by the known technique for making printed circuits. Such spiral-formed printed inductances are disclosed in the French Patent Application No. 2,331,481 and are obtained in particular by engraving upon a thin metallized plate. The widths of the turns of these inductances are not of uniform width in order inter alia to equalize the resistances of the turns. Other printed inductances of the type previously defined have been described in the French Pat. No. 2,118,246. These latter inductances are produced with very fine conductive turns and are engraved upon an intermediate metallized layer which is sandwiched by two metallized layers in order to ensure mechanical protection of both the inductance and the fine strands forming the terminals of the inductance. The entire three layers of this construction produces a printed circuit known as a multilayer circuit. Spiral formed printed inductances have been made by photoengraving and are stacked in order to obtain coupled circuits of band pass type such as those described in the French Pat. No. 1,570,049. These inductances are separated from one another by metal screens provided with slits in order to ensure suitable magnetic coupling between the superimposed inductances. The French Pat. No. 1,476,476 discloses a double-spiralled printed inductance of this type which is formed by two conductive spirals deposited on a flat insulating plate. The internal connecting terminals of the two spirals are connected by a metal filled hole. The spirals are identical and the North magnetic pole of one of spirals and the South magnetic pole of the other spiral face each other.
All of the aforesaid inductances, of spiral-form and printed each upon a plane supporting-plate produce a magnetic field perpendicular to their supporting-plates and for this reason these inductances are poorly adapted for use in telecopier devices or other rapid transcribers. In this type of transcriber device the definition of the points must be of the order of a hundred microns and consequently the distribution of the magnetic field proceeding from the magnetic coupled circuits, requires having a pitch of the order of a hundred microns which is incompatible with the stacking or superimposition in one and the same row of inductances of the known species. The employment of these inductances necessitates a complicated mechanical structure of the reading head of the telecopier from the fact that the width of the inductances is greater than the pitch requested for the reading definition.